With 8:53 left in the fourth quarter Friday, Miles Plumlee left the Suns’ game against the Celtics after being poked in the eye by Kelly Olynyk. The 6-foot-11-inch Plumlee was replaced by 7-1 rookie Alex Len, who picked up 6 points, 3 rebounds, and 1 blocked shot in finishing out the Suns’ 87-80 win.

The Celtics didn’t have anyone to compete with Len, who altered shots, picked up a key putback basket and free throw, and provided a large disruption to the Boston pick-and-roll offense. Having a rim-protecting big man is something the Celtics have lacked for years.

Kevin Garnett played out of position at center. Kendrick Perkins was always undersized and more enforcer than shot blocker while Jermaine O’Neal and Shaquille O’Neal were too old or too injured to provide adequate relief in the middle.

This season the Celtics have lacked a true center. Kris Humphries is a power forward playing center, same with Jared Sullinger. Olynyk has the height of a center but is more of a stretch power forward. Vitor Faverani has true center size but needs development and to get into premium shape to approach being a factor.

Hence the Celtics’ struggles with bigger teams and teams with legitimate impact centers. As the organization begins to transform back to a contender in the coming years, perhaps the team’s No. 1 priority is acquiring a rim protector, a shot-blocking defensive-minded center who can help the Celtics’ defense.

While Len is a rookie and has played just 31 games this season, his length was satisfactory enough to be a major influence.

“Well you know I’ve never had it, but I think it obviously plays a critical role in defending the paint in this league,” Celtics coach Brad Stevens said. “I thought we defended extremely well but we got caught on a switch at the end of the game, which is what we didn’t want to do and as a result they made us pay by [Len] tipping the ball in. Seven-footers can have a big impact on the game in that way and Plumlee is a tough guy to guard because he rolls down the lane so hard. I thought Len gave them good minutes, too.”

Stevens acknowledged he didn’t have that type of center even in his six seasons at Butler. But the Celtics have played all season without a shot-blocking threat or shot-altering big man who can even intimidate opponents.

Said Stevens: “Obviously it’s something that we’ve talked that in an ideal world you have somebody protecting the paint.”

With two first-round picks and salary cap space, the Celtics could make center a main priority. What’s more, a defensive-minded 7-footer could immediately make the Celtics a better defensive team and expedite their rebuilding process.

The Celtics are ninth in the league in points allowed but 21st in rebounding while big men such as Portland’s Robin Lopez, Brooklyn’s Brook Lopez, Indiana’s Andrew Bynum, Houston’s Dwight Howard, and Detroit’s Andre Drummond have dominated the paint in matchups with Boston.

“I haven’t thought a ton about it,” Stevens said. “I think certainly in an ideal situation what you’re looking for is certain qualities of a team and I think that a rim protector, whether it is a seven-footer or not is extremely important in this league, a guy that really protects the paint, dotted line and in.”

Humphries has taken a beating this season serving as the Celtics’ center, although he is just 6-9. Defensively he is trying to check bigger men and offensively, he, like Sullinger, is constantly getting blocked in the paint.

“Well part of the time, it’s a little tougher to rebound sometimes,” Humphries said. “Because if you have a true center and you’ve got to go take him out of the glass, a lot of times you’re taking yourself out of the play.”

When asked if this season he has spent the most time defending centers, he said: “Probably. It’s an adjustment definitely but if I gotta guard them, then they gotta guard me, so I’m able to get some stuff offensively a little bit easier with a five guy guarding you.”

Humphries played the past 3½ years with Brook Lopez, one of the league’s more versatile centers, allowing Humphries to thrive at his natural position.

“Well if you have a true center, he’s banging with the other center and I can run in there and get the rebound and there’s less attention,” he said.

“You have a little more freedom around the basket. The situation [here] is what it is. We’re going to try to finish the year strong. Hopefully people will keep supporting us and coming to these games. I don’t know, I don’t have a lot [more to say].”

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